Method of creating a photonic via using fiber optic

ABSTRACT

A photonic via is made in a substrate by making a hole in the substrate, heating the substrate, and inserting a fiber optic into the hole. In one embodiment, a lens can be made by applying a polymer on top of the photonic via and curing.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The described invention relates to the field of optic integratedcircuits. In particular, the invention relates to a method of forming aphotonic via through a substrate.

[0003] 2. Description of Related Art

[0004] Electronic components are placed on a shared substrate inmulti-chip modules (“MCM”). By packing a number of semiconductor devicesin close proximity to each other, this eliminates the need forindividual packages for each of the devices. Electrical performance isimproved, and board space and cost are reduced.

[0005] In a conventional MCM, the devices are connected to a substrateand the electrical connection among the devices is accomplished withinthe substrate, which may also be an integral part of the MCM package.One of the technologies used to connect the devices to the substrate iscalled flip chip or control collapse chip connection (“C4”). With thistechnology, solder bumps are reflowed to make connection to the terminalpads on the substrate.

[0006] Photonic components, such as, but not limited to, arraywaveguides, amplifiers, couplers, splitters, and other devices forcarrying light-based (“photonic”) signals are manufactured using adifferent process than that for semiconductors. Thus, electroniccomponents and photonic components are manufactured on separatesubstrates using different processes and then interfaced together.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 shows a representation of a substrate having bothelectronic and photonic components.

[0008]FIG. 2 is a flowchart illustrating the process for making asubstrate with both electronic and photonic components.

[0009]FIG. 3 shows a light source such as a vertical cavity surfaceemitting laser (VCSEL) mounted to a substrate and employed to provide aphotonic signal.

[0010]FIG. 4 shows a method of making a photonic via comprising a fiberoptic.

[0011]FIG. 5 shows a cross section of a fiber optic inserted into thesubstrate as described with respect to FIG. 4.

[0012] FIGS. 6A-6D show, in cross-section, an embodiment for making aphotonic via using deposition.

[0013] FIGS. 7A-7C show, in cross-section, a first embodiment for makinga waveguide having an angled surface for redirecting a photonic signal.

[0014] FIGS. 8A-8E show, in cross-section, a second embodiment formaking a waveguide having an angled surface for redirecting a photonicsignal.

DETAILED DESCRIPTION

[0015]FIG. 1 shows a representation of a substrate 10 having bothelectronic 12 and photonic 14 components. In one embodiment, theelectronic components 12 include a light source for generating aphotonic signal from an electrical input. The photonic signal istransmitted to the photonic components 14 on the other side of thesubstrate 10. In one embodiment, a housing 16 may be used to cover oneor more of the electronic components, the photonic components and/or thesubstrate. A heat sink 18 may be used to help cool the components.

[0016] In one embodiment, a light source such as an edge emitting laser(EEL) 20 is used to produce a photonic signal. The EEL may be coupledvia a fiber optic 22 (also called an “optical fiber”) around thesubstrate 10 to a waveguide 24 or other photonic component on the otherside of the substrate 10.

[0017]FIG. 2 is a flowchart illustrating the process for making asubstrate with both electronic and photonic components. Because thephotonic components require elevated temperatures of up to 900-1100degrees C., the photonic side is processed first (box 102). It should benoted that standard semiconductor processes go up to approximately 230degrees C., above which insulative and passivation layers comprising,e.g, polyimide, may be damaged.

[0018] Processing of the photonic components may include creating awaveguide, which is described in more detail with respect to FIGS. 7A-7Cand 8A-8E. After the photonic components are processed, the electronicinterconnections are made on the substrate (box 104). Electroniccomponents are attached to the substrate through solder and flip chip(C4) solder bumps.

[0019]FIG. 3 shows a light source such as a vertical cavity surfaceemitting laser (VCSEL) 50 mounted to a substrate 10 and employed toprovide a photonic signal 60. The VCSEL 50 produces a vertical cone oflight. In one embodiment, the VCSEL is mounted on one side of thesubstrate using the flip chip (or C4) technology employing solder bumps.The VCSEL 50 is lithographically aligned on the substrate to provide aphotonic signal 60 through the substrate to a photonic component such asa waveguide 64 on the other side of the substrate.

[0020] In one embodiment, an angled surface 68 is used to re-direct thephotonic signal 60 from the VCSEL 50 through the waveguide 64 byreflecting the photonic signal approximately 90 degrees. In thisembodiment, the angled surface makes an approximate 45 degree angle withthe surface of the substrate and is part of the waveguide itself. Amethod for making the angled surface in the waveguide is described withrespect to FIGS. 7A-7C and 8A-8E.

[0021] A “photonic via” is employed to couple the light source with thephotonic component on the other side of the substrate. In oneembodiment, reactive ion etching (“RIE”) is used to make a hole in thesubstrate. RIE allows for anisotropic vertical etching. In the simplestembodiment, an air-filled photonic via couples the light source with thephotonic component. However, photonic vias can also be made out ofstandard optical materials including, but not limited to, glass, oxides,and polymers.

[0022]FIG. 4 shows a method of making a photonic via comprising a fiberoptic. In one embodiment, a hole is made in a substrate using an etch orother method (box 202), then the substrate is heated (box 204). The holeexpands due to the temperature, and a fiber optic is then inserted intothe hole (box 206). When the substrate cools back to room temperatureand the hole shrinks, the fiber optic is held firmly in place. In oneembodiment, the substrate is heated to approximately 150-200 degrees C.,but the temperature depends on the coefficient of thermal expansion ofthe substrate and also depends on how well the fiber optic is held inplace after the substrate cools down.

[0023]FIG. 5 shows a cross section of a fiber optic 220 inserted intothe substrate 222 as described with respect to FIG. 4. After the fiberoptic 220 is inserted into the substrate, the end of the fiber optic 220may be polished to provide a better optical coupling. A lens 250 can beadded as will be described later.

[0024] FIGS. 6A-6D show, in cross-section, an embodiment for making aphotonic via using deposition. In FIG. 6A, a hole or trench 232 is madein the substrate 230. RIE may be used to make the hole, as previouslydescribed. A cladding 236 is then deposited as shown in FIG. 6B. In oneembodiment, the cladding material is an oxide that is evenly depositedover the entire substrate to a predetermined thickness using chemicalvapor deposition (CVD). An optical core material 240 having a higherindex of refraction than the cladding material is then deposited andfills the rest of the hole, as shown in FIG. 6C. In one embodiment, theoptical core material is a polymer, but oxides may be employed also. Apolishing step can be applied to provide a better optical coupling forthe photonic via. Polishing may also be used to eliminate the claddingfrom the surfaces of the substrate as shown in FIG. 6D.

[0025] Additionally, the technique of FIGS. 6A-6D may be employed to notonly couple components on opposite sides of a substrate but to couplephotonic components, one or both of which may be internal to thesubstrate.

[0026] A further enhancement to the fiber optic photonic via and thedeposition photonic via of FIGS. 4, 5 and 6A-6C is to form a lens tobetter direct light into the photonic via. One method of forming a lensis to apply polymer to the end of the photonic via. As the polymer iscured, a lens 250 is formed, as shown in FIGS. 5 and 6D. By modifyingthe amount of material used in the lens and the cure time, differentshapes may be produced.

[0027] In one embodiment, a light source such as a VCSEL having awavelength of approximately 1550 nm is used to provide a photonic signalthrough a silicon substrate. Silicon is transparent to light having awavelength of approximately 1550 nm, so no physical via is needed. The“photonic via” in this case is directly through the solid siliconsubstrate.

[0028] FIGS. 7A-7C show, in cross-section, a first embodiment for makinga waveguide having an angled surface for redirecting a photonic signal.FIG. 7A shows a photonic via 302 in a substrate 300. The photonic viamay be made by one of the methods previously described.

[0029]FIG. 7B shows a layer of cladding 310 that is deposited on thesubstrate 300. In one embodiment, the cladding is SiO₂ that is thermallygrown on the substrate 300 and then etched to be lithographicallyaligned to the edge of the photonic via 302. Alternatively, the cladding310 could be formed by other methods of deposition and etching.

[0030]FIG. 7C shows a layer of optical core material 330 deposited overthe cladding 310 and the substrate 300. In one embodiment, the opticalcore material 330 is deposited by high density plasma (HDP) deposition.Due to the different heights of the substrate 300 and the cladding 310,the optical core material 330 forms an angled surface 320 that makes anapproximate 45 degree angle with the substrate surface. In oneembodiment the optical core material 330 is glass, but it couldalternatively be a polymer or other material. The optical core material330 also forms a waveguide by trapping light that enters the sectionbetween the cladding 310 and the outside air 340. In one embodiment, theoptical core material of the angled surface and waveguide is either ofthe same material as that of the photonic via or has a similar index ofrefraction.

[0031] FIGS. 8A-8E show, in cross-section, a second embodiment formaking a waveguide having an angled surface for redirecting a photonicsignal. FIG. 8A shows a substrate 400 with a cladding 410 deposited onit. A photonic via 402 goes through the substrate 400 and the cladding410. FIG. 8B shows a layer of optical core material 412 deposited ontothe cladding 410 and photonic via 402. A mask 414 is then deposited ontop of the optical core material 412, as shown in FIG. 8C. In oneembodiment the mask comprises silicon nitride, but other materials mayalso be used.

[0032]FIG. 8D shows the waveguide after an etch is applied which causesthe optical core material to form an angled surface 420. In oneembodiment, a wet isotropic etch is employed; however, an isotropic dryetch may alternatively be employed. The mask can then be stripped offusing another etch, as shown in FIG. 8E. Because of the dual masks 414,two waveguides each with its own angled surface is achieved. Of coursemaking a single waveguide and a single angled surface is also easilyachieved by modifying the mask layer.

[0033] The angled surfaces of FIGS. 7A-7C and 8A-8E are able to redirectphotonic signals from the photonic via into the waveguide, as wasdescribed with respect to FIG. 3. By lithographically aligning a lightsource with the waveguide, much time is saved and efficiency is improvedfrom manual alignment.

[0034] Thus, a method for creating a photonic via using a fiber optic isdisclosed. However, the specific embodiments and methods describedherein are merely illustrative. Numerous modifications in form anddetail may be made without departing from the scope of the invention asclaimed below. The invention is limited only by the scope of theappended claims.

What is claimed is:
 1. A method of making a photonic via comprising:making a hole in a substrate; inserting a fiber optic into the hole. 2.The method of claim 1 further comprising: heating the substrate prior toinserting of the fiber optic.
 3. The method of claim 2 furthercomprising: using an etching process to make the hole in the substrate.4. The method of claim 3 further comprising: using a reactive ion etchto make the hole in the substrate.
 5. The method of claim 2 furthercomprising: depositing a polymer on top of the fiber optic; and curingthe polymer to form a lens over the fiber optic.
 6. The method of claim2 further comprising: polishing an end of the fiber optic.
 7. A methodof making a photonic via comprising: etching a hole in a substrate;heating the substrate; and inserting a fiber optic into the substrate.8. The method of claim 7, wherein the fiber optic is an optical corematerial enclosed in a cladding.
 9. The method of claim 8 furthercomprising: forming a lens on top of the fiber optic.
 10. The method ofclaim 9 further comprising: depositing a polymer on top of the fiberoptic; and curing the polymer to form the lens over the fiber optic. 11.The method of claim 8 further comprising: polishing an end of the fiberoptic.
 12. A method of making a photonic via comprising: etching a holein a silicon substrate; heating the silicon substrate; and inserting afiber optic into the silicon substrate.
 13. The method of claim 12further comprising: polishing an end of the fiber optic.
 14. The methodof claim 12 further comprising: forming a lens on top of the fiberoptic.
 15. The method of claim 14 further comprising: depositing apolymer on top of the fiber optic; and curing the polymer to form thelens over the fiber optic.